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<H3>bound_modify command 
</H3>
<P><B>Syntax:</B>
</P>
<PRE>bound_modify wall1 wall2 ... keyword value ... 
</PRE>
<UL><LI>wall1,wall2,... = <I>xlo</I> or <I>xhi</I> or <I>ylo</I> or <I>yhi</I> or <I>zlo</I> or <I>zhi</I> 

<LI>one or more keyword/value pairs may be listed 

<PRE>keywords = <I>collide</I> or <I>react</I>
  <I>collide</I> value = sc-ID
    sc-ID = ID of a surface collision model
  <I>react</I> value = sr-ID
    sr-ID = ID of a surface reaction model or none 
</PRE>

</UL>
<P><B>Examples:</B>
</P>
<PRE>bound_modify yhi collide 1 react 2
bound_modify zlo zhi collide hotwall 
</PRE>
<P><B>Description:</B>
</P>
<P>Set parameters for one or more of the boundaries of the global
simulation box.  Any of the 6 faces can be selected via the list of
<I>wall</I> settings.
</P>
<P>The <I>collide</I> keyword can only be used when the boundary is of type
"s", for surface, as set by the <A HREF = "boundary.html">boundary</A> command.
This keyword assigns a surface collision model to the boundary, as
defined by the <A HREF = "surf_collide.html">surf_collide</A> command.  The ID of
the surface collision model is specified as <I>sc-ID</I>, which is the ID
used in the <A HREF = "surf_collide.html">surf_collide</A> command.
</P>
<P>The effect of this keyword is that particle collisions with the
specified boundaries will be computed by the specified surface
collision model.
</P>
<P>The <I>react</I> keyword can only be used when the boundary is of type "s",
for surface, as set by the <A HREF = "boundary.html">boundary</A> command.  This
keyword assigns a surface reaction model to the boundary, as defined
by the <A HREF = "surf_react.html">surf_react</A> command.  The ID of the surface
reaction model is specified as <I>sr-ID</I>, which is the ID used in the
<A HREF = "surf_react.html">surf_react</A> command.  If an sr-ID of <I>none</I> is used
then surface reactions are turned off.
</P>
<P>The effect of this keyword is that particle collisions with the
specified boundaries will induce reactions which are computed by the
specified surface reaction model.
</P>
<P><B>Restrictions:</B>
</P>
<P>For 2d simulations, the <I>zlo</I> and <I>zhi</I> boundaries cannot be modified
by this command, since they are always periodic.
</P>
<P>All boundaries of type "s" must be assigned to a surface collision
model via the <I>collide</I> keyword before a simlulation can be performed.
Using a surface reaction model is optional.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "boundary.html">boundary</A>, <A HREF = "surf_modify.html">surf_modify</A>
</P>
<P><B>Default:</B>
</P>
<P>The default for boundary reactions is none.
</P>
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